Resolution of racemic compounds is becoming an increasingly important industrial function for the last several years. This is because the resolved compounds, the optically active D or L isomers, have valuable utility and applications in fields such as, for example, drugs, fragrances, electronics and the like. Particularly in the pharmaceutical field, there is a great interest in optically active isomeric forms of drugs. See, for example, Chiral Drugs, S. C. Stinson, Chemical & Engineering News, American Chemical Society, Washington, DC, 44 (Oct. 9, 1995); idem, ibid., 38 (Sep. 27, 1993); and Chiral Drugs fast entering the Mainstream, Chemical Marketing Reporter, 5 (Jun. 10, 1996).
Obtaining optically active (chiral) isomeric forms of compounds has been traditionally achieved by processes such as, for example, chiral synthesis, asymmetric hydrogenation of appropriate precursors, enzymatic resolution, chromatic processes, and the like. However, such traditionally available synthetic methods to resolve racemates generally involve complicated or selective chemical reactions which necessitate a subsequent reverse reaction to yield the desired enantiomer; many of them are expensive and the yields are not always satisfactory. The enzymatic processes are generally slow. Since most chemical reactions result in the formation of racemates, an economical approach to resolving such readily available racemates would be the cheapest and easiest way to obtain chiral isomers.
Among chiral compounds, chiral amino acids are important commercial materials. Many resolution methods, particularly for amino acids, involve salt formation using resolving agents and reconversion. Many of these resolving agents are generally expensive. Among non-salt forming methods, ligand exchange chromatography has been proposed. Even here prior derivatization of the amino acid is sometimes necessary. See, for example, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc., New York, vol. 2, 521 (1992). Thus, there is a growing interest in finding inexpensive ways to resolve racemic mixtures into optically active isomers.
It is, therefore, an object of this invention to provide a viable process to resolve racemates into optically isomers.
It is another object of this invention to provide a process to separate racemates into optically active isomers without the need for salt formation.
It is yet another object of this invention to provide a process to separate racemic amino acids into optically active isomers.
Other objects and advantages of the present invention will be apparent from the accompanying summary, description and examples.